MRSA, a spherical Gram-positive aerobe, accounts for up to 50% of nosocomial S. aureus infections, and represents a multi-billion dollar problem in critical care units, intensive care units and general hospitals worldwide. Because bacteria naturally adapt to antibiotics, more than 95% of patients with MRSA do not respond to first-line antibiotics. Certain MRSA strains are now even resistant to glycopeptide antibiotics like Vancomycin®, removing the last remaining effective antibiotic treatment for the disease. Due to the fact that MRSA is resistant to most antibiotics such as methicillin, oxacillin, penicillin and amoxicillin, there is a need to treat MRSA without the use of antibiotics.
Photodynamic disinfection is a desirable alterative treatment method as it has been demonstrated to be an effective non-antibiotic antimicrobial approach in vitro. One exemplary advantage of photodynamic disinfection as a MRSA treatment modality is that, due to this non-specific bactericidal mechanism, it is typically not subject to issues of resistance that can plague the use of antibiotics. As another exemplary advantage, it can be employed as a localized topical treatment that can be administered in areas such as the nasal cavities (e.g., nasal mucosa) where MRSA is mostly likely found in the human body.
Photodynamic disinfection fundamentally involves the use of light energy to activate one or more photosensitizers of a photosensitizing composition so that those photosensitizers can then either pass energy on directly to a substrate/target (type I reaction), or can interact with molecular oxygen to produce reactive oxygen species (type II reaction). These reactions mediate the non-specific reduction of MRSA and other microbial cells primarily via lipid peroxidation, membrane damage, and damage to intracellular components.